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Nov. 27, 1956 A. E. CANFORA Re. 24,

ELECTRONIC PHASE SHIFTING s sma Original Filed' June 11, 1951 2 Sheets-Sheet l v INVENTOR Nov. 27, 1956 A. E. cANFo'RA 24,240

ELECTRONIC PHASE snmmc svs'rzu Orig1nal Filed June 11, 1951 2 Sheets-Sheet 2 l FA Fgz HDIL Lt, cum/v a 4 Z a a fpurorf INVENIOR filial/Ewan ATTORNEY v ied Sm l 135 m 2 4,240 ELECTRONIC PHASE SHIFTING SYSTEM Arthur E. Canfora, Brooklyn, N. Y., assignorto Radio Corporation of America, a corporation of Delaware OriginalNo. 2,636,984, datetl'April '28, 1953, Serial No. 230,891, June 11, 1951. Application for reissue'March 24, 1954, Serial No. 418,800

12 Claims. (Cl. 250-27) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printedin italics indicates the additions made by reissue.

The present invention relates to. phase shifting systems, and, more particularly, to a novel system for retarding the phase of a square Wave in controlled increments. The invention is particularly suited for 'use with a frequency divider of the binary o'r multivibrator type in which areset or feedback pulse is applied from one stage to a preceding stage to shift the output frequency between two discrete limits.

In atypical frequency divider of'the'binary or multivibrator type comprising two multivibrator counter stages, the output from one side of the following stage is suitably fed back to one side of the preceding stage to reduce the dividing factor or count. A two-stage counter or frequency divider will normally divide by four. With feedback, it will divide by three. In accordance with this invention, the feedback path includes an amplifier'which 'can be controlled to omit a feedback pulse or pulses. A separate multivibrator of the single shot type controls the feedback tube in one or more predetermined ways to effect phase shift of the input wave to the frequency divider. A suggested use of the invention is to neutralize a constantly occurring unidirectional phase displacement between a local source and 'a signal received from a more or less remote point. This situation'may be presented in the operation'of facsimile and. printing telegraph apparatus.

An object of the present invention is to provide novel means'for controlling a frequency divider having a pulse feedback path by rendering the feedback path ineffective in a predetermined interval or intervals.

A further object is to provide novel means for alteringthe phase of an electrical wave formation under control of correction pulses.

Otherobjects and advantages of the invention will, of course, become apparent and-immediately suggest themselves to those skilled in the art to which this invention is directed from a reading of the following specification in connection with the accompanying drawing in which:

Fig. 1 is a schematic" showing of phase shifting apparatus embodying the present invention;

, Fig. 2, sections a through c, shows a set'of explanatory curves; "and Fig. '3, sections a to d, shows a corresponding set of curves illustrating onemode of operation of the invention.

Fig. 1 of the drawing shows, illustratively, apparatus embodying the invention for shifting the phase of an output square wave (Fig. 2c). The input wave 10 is fed to a frequency divider made up of two multivibrators or trigger circuits 12 and 14 in the illustrative example. The multivibrators and their connections are known in the art. Electronic apparatus employing multivibrators similar tothose shown illustratively in Fig. 1 of the drawing is discussed in an article-entitled Electronic digital count- Riissued Nov. 27, 1956 ers by Warren H. Blissappearing in the April 1949 issue of Electrical Engineering. Suitable multivibrator drive circuits are also shown in U. S. Patent No."2,478,- 6S3 granted to \Narren H. Bliss, August 9, 1949.

The multivibrator 12 is in the form of a flip-flop or locking multivibrator having twotubes 16 and 17 coupled as shown. This multivibrator has two stable states. The resistor-condenser combinations 18 and 19, one in each cross-coupling circuit, control the switching time of the multivibrator. The pulsating input wave -10-is applied to a terminal 21 and after ditferentiationbya condenser 26 and resistor 28, is applied to the plate of the tube 16. Likewise, the input wave is differentiated by'the condenser 31 and the resistor 32 for application to the plate of the tube 17. The negative-going pulses applied to these plates'cause reversal of the multivibrator stage 12, which in normal operation wouldprovide a square wave of one-half the frequency of the input wave 10. The output from the multivibrator stage 12 is taken from the'plate of the tube 17 and is-dilferentiated by a condenser 34 and-a resistor36-for application to the plate of the tube 38 of the multivibratorstage-14. Also, the output from the multivibrator stage 12 is differentiatedby a condenser 41 and a resistor42 for application to the plate of the tube 43. The output of the multivibrator stage 14 appears across terminals 46 "and 47. With the arrangement thus far described, the-output frequency would be the frequency of the input wave 10 divided by four. Referring to Fig. 2c, it is seen that the actual output frequency, because of the reset-action to be described, is onethird of the frequency ofthe'wave'10.

The feedback to or reset of the multivibrator stage 12 is accomplished over a connection 48 which includes a condenser 51 and a resistor 52 for ditferentiating the square wave output from the plate ofthe tube 43. A tube '54 is provided, the grid of which is'maintained below cutoff by a negative-bias voltage applied at the terminal 56 of the grid resistor 58. Any suitable biasing source (not shown) may be used. The grid resistor 58 is shunted by a grid condenser 59. The-plate 61 of the tube'54 is connected to the plate of the tube 16 of thefrequency divider stage 12. The negative biasing voltage on the grid of the tube 54 is so chosen that thepositive pulses from the differentiated transitions occurring at the plate of the tube 43 can cause the tube 54' to conduct and therebyresetthe binary frequency dividing stage 12. This reset action occurring periodically causes a division of the frequency of the input wave 10 by three as shown by Figs. 2b and 2c.

Fig. 3 illustrates the elimination of one of the reset pulses 63' appearing in Fig. 2e. These'reset pulses extend inthe positive direction above the cut-off point of the grid of the tube 54. *A siugle-sho'flor unbalanced multivibrator 66 comprising tubes'63 and 69 is provided. A mnltivibrator of this type is disclosed in Patent No. 2,428,- 92dgranted0ctober'l4, 1947 to Warren H. Bliss. The grid resistor 72 for the gridof the'tube 69 is adjustable so that the time duration of therpulse'produced by this multivibrator may be controlled. The grid of the tube 63 is connected to the/plate of the tube'69 through a direct-current path includinga resistor 74. The cross-connection between the plate of the tube 68'and'the grid of the tube 69 includes a condenser 76. Retard information which may,.illustratively, be m the form ofperiodic pulses or a square wave. of the desired frequency is applied to the plate-of the tube-68 from a'terminal 78. Where correction-orneutralization of a constantly occurring phase displacement'between a" local source and an incoming signal is required,'the:frequency of the wave or theperiodicity'ofnthe seriesof puls'es applied to the terminal 78 will be relatively constant. Where a square wave is applied to the terminal 78, a condenser 81*a-nd 3 a resistor 82 differentiate this wave before it is applied to trigger the multivibrator 66.

In the latter, the tube 69 is normally conducting and the tube 68 is non-conductive. When no retard information is being received, the potential at the plate ofthe tube 68 is relatively constant as shown by Fig. 2d. All of the reset pulses 63 will therefore be repeated in the plate circuit of the tube 54. The multivibrator 66, when tripped, remains triggered for a time which is equivalent to the time between two of the normal reset pulses 63. This time duration of the operation of the trigger circuit 66 is so chosen because it ensures the elimination of a single normal reset pulse 63.

When the multivibrator 66 triggers, the plate of the tube 68 undergoes a potential decrease. This condition is illustrated in Fig. 3c. The decrease in potential in the plate of the tube 68 is impressed, in part, upon the grid of the tube 54 making its grid go more negative than the cut-off point so that the normal reset pulse occurring during the trigger time of the multivibrator 66 cannot cause the tube 54 to conduct and reset the first multivibrator 12. In this way, the object of retarding the output wave is accomplished. In the illustrative arrangement, the retardation is 120 electrical degrees as shown by Fig. 3b. The trigger time of the multivibrator 66 may be such as to eliminate two or more of the reset pulses for a greater retardation time.

The trigger circuit 66 as shown may be replaced by a controlled locking circuit similar to the multivibrator 12 or 14 so as to permanently change the order of division between two discrete numbers. The output frequency would vary between f/3 and f/4. This would apply for frequency shift keying, for example.

The insertion of an extra reset pulse into the multivibrator 12 will effect an advance of phase of the output wave.

What is claimed is:

1. Phase shifting apparatus comprising means to pro- I vide an alternating current input signal of square wave form, a plurality of multivibrators for performing a frequency division on said signal whereby to provide an output signal from said multivibrators, a feedback [link] path for feeding reset pulses from one of said multivibrators to another, and means responsive to a retarding signal for interrupting transmission of said reset pulses whereby to retard the phase of said output signal.

2. Phase shifting apparatus comprising means to provide an alternating current input signal of square wave form, a chain of two coupled bistable multivibrators for performing a frequency division on said signal, said chain normally dividing said signal frequency by four, a feedback [link] path for feeding reset pulses from one multivibrator to the other, whereby to provide an output signal from said multivibrators of a frequency which is onethird of the frequency of the input signal, and means responsive to a retarding signal for interrupting transmission of said reset pulses whereby to retard the phase of said output signal.

3. Phase shifting apparatus comprising means to pro vide an alternating current input signal of square wave form, a multivibrator having two stable conditions of operation, means to apply said input signal to said multivibrator, a second multivibrator having two stable conditions of operation, means to couple the output of said first multivibrator to said second multivibrator, a feedback connection from said second multivibrator to said first multivibrator whereby to alter the frequency division of said multivibrators, a third multivibrator of the unbalanced type, means to apply pulses to said third multivibrator in accordance with retard information, and means operating under control of said third multivibrator for disabling said feedback connection during the time of reversal of said third multivibator whereby to retard the phase of the output signal from said second multivibrator. I i

4. Phase shifting apparatus comprising means to provide an alternating current input signal of square wave form, a multivibrator having two stable conditions of operation, means to apply said input signal to said multivibrator, a second multivibrator having two stable conditions of operation, means to couple the output of said first multivibrator to said second multivibrator, a feedback connection including a vacuum tube from said second multivibrator to said first multivibrator whereby to alter the frequency division of said multivibrators, a third multivibrator of the unbalanced type, means to apply pulses to said third multivibrator in accordance with retard information, and means operating under control of said third multivibrator for biasing said vacuum tube below cut-off during the time of reversal of said third multivibrator whereby to retard the phase of the output signal from said second multivibrator.

5. Phase shifting apparatus comprising means to provide an alternating current input signal of square wave form, a multivibrator having two stable conditions of operation, means to apply said input signal to said multivibrator, a second multivibrator having two stable conditions of operation, means to couple the output of said first multivibrator to said second multivibrator, a feedback connection including a vacuum tube from said second multivibrator to said first multivibrator to feed back reset pulses whereby to alter the frequency division of said multivibrators, a third multivibrator of the unbalanced type having a time of operation substantially equal to the time between two reset pulses, means to apply pulses to said third multivibrator in accordance with retard information, and means operating under control of said third multivibrator for disabling said feedback connection during the time of operation of said third multivibrator whereby to eliminate one feedback pulse and re tard the output from said second multivibrator.

6. Phase shifting apparatus comprising means to provide an input signal of pulsating waveform, a plurality of multivibrators arranged in series for performing a frequency division on said signal in order to provide an output signal from said multivibrators, a feedback path for feeding reset pulses from one of said multivibrators to another, a source of control signal other than said output signal, and an electronic device in said feedback path responsive to said control signal for altering transmission of said reset pulses thereby to shift the phase of said output signal.

7. Phase shifting apparatus comprising means to provide an input signal of pulsating waveform, a plurality of multivibrators for performing a frequency division on said signal in order to provide an output signal from said multivibrators, a feedback path for feeding reset pulses from one of said multivibrators to another, a source of control signal other than said output signal, and means responsive to said control signal for altering transmission of said reset pulses thereby to shift the phase of said output signal with respect to said input signal.

8. Frequency shifting apparatus comprising means to provide an input signal of pulsating waveform, a plurality of multivibrators for performing a frequency division on .aid signal in order to provide an output signal from said multivibrators, a feedback path for applying reset pulses from one of said multivibrators to another, a source of control signal other than said output signal, and means responsive to said control signal for interrupting transmission of said reset pulses thereby to shift the frequency of said output signal between two discrete frequencies.

9. Frequency shifting apparatus comprising means to provide an input signal of pulsating waveform, a plurality of multivibrators for performing a frequency division on said signal in order to provide an output signal from said multivibrators, a feedback path for applying reset pulses from one of said multivibrators to another, a source of control signal other than said output signal, and means interposed in said feedback path and responsive to a periodic pulse signal from said source of control signal for altering transmission of said reset pulses thereby to shift the frequency of said output signal between two discrete frequencies.

10. Phase shifting apparatus comprising means to provide an input signal of pulsating waveform, a plurality of multivibrators arranged in series for performing a frequency division on said signal in order to provide an output signal from said multivibrators, a feedback path including a difierentiating circuit for feeding reset pulses from one of said multivibrators to another, and an electronic device in said feedback path responsive to a phase shifting signal for altering transmission of said reset pulses and thereby to shift the phase of said output signal.

11. Phase shifting apparatus comprising means to provide an input signal of pulsating waveform, a plurality of multivibrators arranged in series for performing a frequency division on said signal in order to provide an output signal from said multivibrators, a diflerentiator between the output of each multivibrator and the input of the immediately succeeding multivibrator, a feedback path including a difierentiator circuit for feeding reset pulses from one of said multivibrators to another, and an electronic device in said feedback path responsive to a phase shifting signal for altering transmission of said reset pulses thereby to shift the phase of said output signal.

12. Phase shifting apparatus as claimed in claim 11 wherein said plurality of multivibrators are an even 10 number.

References Cited in the file of this patent or the original patent UNITED STATES PATENTS 15 2,492,736 Custin Dec. 27, 1949 2,521,774 Bliss Sept. 12, 1950 2,549,505 Mohr Apr. 17, 1951 2,564,559 Canfora Aug. 14, 1951 

